vhost-user-blk device (snapshot support)

[kalyazin]

Feature Request

Add snapshot support for vhost-user-blk devices.

Describe the desired solution

Firecracker implements saving and restoring from snapshot VMs that have block devices backed by vhost-user attached.

Describe possible alternatives

The status quo is VMs having vhost-user-blk devices cannot be snapshotted. We can leave it as is.

Additional context

vhost-user-blk basic support

Checks

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[kalyazin]

Moving the issue back to "Researching" state, because we have currently paused investment in the technology since performance testing did not demonstrate clear gains against our current solution.